Vacuum cleaners or robotic vacuum cleaners have certain shapes in a region in contact with the surface to be cleaned in order to gather and transport the usually solid dust and dirt particles using certain physical principles. An important principle is the pulsed solid contact between the brush filaments and the floor being worked on in each case, as well as the dirt particles found thereon. In this way, said dirt particles are mobilised and transported.
The frequently round or substantially round basic shape of robotic vacuum cleaners makes it difficult to reach dirt particles in corners. In order to increase the surface-cleaning capacity, it is therefore of particular importance, especially in robotic vacuum cleaners, for the regions to the right and left of the suction mouth itself to be worked on by assistive side brushes which protrude beyond the diameter of the housing. An essential aim of such side brushes and the bristle clusters thereof is to solely mechanically move dirt particles found on the floor using the brush filaments of the bristle clusters and to deliver them to the suction mouth.
Such side brushes are known, for example from EP 2 606 798 A2. Known side brushes comprise just a few regularly spaced brush arms in the form of paintbrush-like brushes, that is to say bristle clusters or sleeves having bristle clusters fastened therein. The known side brushes comprise two, three, four or five brush arms of this type, and in any case comprise few brush arms.
The drawback of such side brushes is primarily the unsatisfactory surface coverage. This results firstly from the fact that a side brush comprises just a few bristle clusters, so that a drop sensor positioned in the movement region of the bristle clusters is not, or at least not unnecessarily, disrupted. A drop sensor of this type is provided, in a known manner, for detecting steps or other drops in the surface, and said drop sensor operates on the basis of a reflection of light signals emitted towards the floor which is detected by means of a sensor system in each case. In a drop sensor positioned in the movement region of the bristle clusters of a side brush, the bristle clusters of a rotating side brush either interrupt the beam path from the light source or the beam path to the sensor system. Such an interruption to the beam path results in a reduction in the quantity of light arriving at the sensor system, and therefore a differentiation cannot readily be made between such an interruption and a reflection of light which does not occur owing to a step or the like being located in front of the robotic vacuum cleaner. Such a differentiation can only be made for a few bristle clusters by taking into account the time profile of a signal received by the sensor system and by a conclusion being drawn on a situation in which a fall is likely if, for example, an amount of light arriving at the sensor system over a relatively long time period is below a threshold value. However, the unsatisfactory surface coverage also results from the fact that, for example in a robotic vacuum cleaner, the speed when moving over a portion of floor to be worked on in each case is so high relative to the rotational speed of the side brushes that the areas covered by the individual bristle clusters are several millimeters to several centimeters apart. This leads to dirt, such as individual crumbs or the like, not being gathered by the side brushes and remaining on the surface to be cleaned.
In general, the driving speed of the robotic vacuum cleaner should not be reduced because otherwise the surface area performance of the robotic vacuum cleaner decreases. Likewise, the quantity of bristle clusters of a side brush cannot readily be increased owing to the requirement for detecting falls. Similarly, the position of the drop sensor cannot readily be modified because it is necessary for the drop sensor to always be located at a certain distance in front of and laterally next to a driven or non-driven wheel of the robotic vacuum cleaner. The required position of the drop sensor in this respect results in the drop sensor being positioned in the movement region of the bristle clusters.